The Media Access Control sublayer of layer 2 of the OSI model. The MAC is addressed by the IEEE 802.3 standard. The MAC sublayer defines the way that devices on the network share the network medium. Also the data link layer implements MAC protocols to ensure that nodes have the opportunity to transmit but do not conflict.

An erasable,high-capacity,removable storage device similar to a CD-ROM drive.
MO drives use both magnetic and laser technology to write data to the disk, and use the laser to read that data back again.

The mail program used by the end-user computer to create and read e-mail messages. The MUA passes the message to the local MTA.

mainframe computer

A large,fast multi-user computer system,designed to manage very large amounts of data and very complex computing tasks. Mainframes are normally installed in large corporations, universities, or military installations, and can support hundreds, even thousands ,of users.

maintenance release

A software upgrade that corrects minor bugs or adds a few small features, distinguished from a major release by an increase in only the decimal portion of the version number--i.e., from 3.0 to 3.1, rather than from 3.1 to 4.0

male connector

Any cable connector with pins designed to engage the sockets on the female part of the connector.

Maltron keyboard

An alternative keyboard designed to eliminate carpal tunnel syndrome that arranges the keys in two concave areas conforming to the shape of the hand, allowing better alignment of the forearm and wrist.

Controls the rate of reference time within a graph and is used by filters within the graph to synchronize presentation times. Provides a standard mechanism to query the reference time, to query the physical clock time and rate (compared to the system clock) of the owner of the master clock, and to establish event notifications based on position changes in the master clock's reference time.

Multicast Backbone, An experimental method of transmitting digital video over the Internet in real time.
The TCP/IP protocols used for Internet transmissions are unsuitable for real time audio or video; they were designed to deliver text and other files reliably, but with some delay. MBONE requires the creation of another backbone service with special hardware and software to accomodate video and audio transmissions; the existing Internet hardware cannot manage time-critical transmissions. This information may be out of date at the present time.

Micro Channel Architecture. A 32-bit proprietary expansion bus first introduced by IBM in 1987 for the IBM PS/2 range of computers, and also used in the RS/6000 series.
MCA is incompatible with expansion boards that follow the earlier 16-bit AT bus standard, physically because the boards are about 50 percent smaller, and electronically as the bus depends on more proprietary integrated circuits.
MCA was designed for multiprocessing, and it also allows expansion boards to identify themselves, thus eliminating many of the conflicts that arose through the use of manual settings in the original bus.

MCD

Miniclient driver. An OpenGL driver model in which the driver is responsible only for handling those features that can be accelerated in hardware, leveraging software implementation to handle the rest of the pipeline.

Monochrome Display Adapter. A video adapter introduced in 1981 that could display text but not graphics, in one color, at a resolution of 640 pixels horizontally by 350 vertically. MDAs were replaced in many cases by the Hercules Graphics Card

MDL

Memory descriptor list. In Windows NT® and Windows 2000, an opaque structure, defined by Memory Manager, that uses an array of physical page frame numbers to describe the pages that back a virtual memory range.

Abbreviated M. A prefix meaning one million in the metric system. Because computing is based on powers of 2, in this context mega usually means 220or 1,048,576; the power of 2 closest to 1 million bits.

megabit

Abbreviated mbit. Usually 1,048,576 binary digits or bits of data. Often used as equivalent to 1 million bits.

Megabits per second

A measurement of the amount of information moving across a network or communications link in one second, measured in multiples of 1,048,576 bits.

One million cycles per second. A processor's clock speed is often expressed in MHz.

membrane keyboard

A pressure-sensitive keyboard covered by a protective plastic sheet used in a hostile environment where operators may not always have clean hands. While it is very difficult to type quickly and accurately on a membrane keyboard, they are most often used for occasional data entry in factories or in fast food restaurants.

memory

The primary random-access memory (RAM) installed in the computer.
The OS copies application programs from disk into memory, where all program execution and data processing takes place; results are written back out to disk again. The amount of memory installed in the computer can determine the size and number of programs that it can run, as well as the size of the largest data file.

memory address

The exact location in memory that stores a particular data item or program instruction.

memory board

A printed circuit board containing memory chips. When all the sockets on a memory board are filled, and the board contains the maximum amount of memory that it can manage, it is said to be "fully populated."

memory cache

An area of high-speed memory on the processor that stores commonly used code or data obtained from slower memory, replacing the need to access the system's main memory to fetch instructions.

memory chip

A chip that holds data or program instructions. A memory chip may hold its contents temporarily , as in the case of RAM, or permanently as in the case of ROM.

memory management

The way in which the computer handles memory. In the PC you may find the following kinds of memory:

Conventional memory: This is the area of memory below 640KB

Upper memory:Also known as reserved memory. The 384KB of memory between 640KB and 1MB. This space is used by system hardware such as the video adapter. Unused portions of upper memory are known as upper memory blocks (UMBs), and on some PCs UMBs can be used for loading device drivers or terminate-and-stay-resident programs.

A file that contains information about other files, particularly those used for data interchange. Metafiles often have the file name .MET

method set

Used in Windows NT, Windows 2000, and WDM drivers to perform an action, such as allocating memory, and to provide a way to access related actions. Each method set has a unique identifier used to retrieve that method set and can be fulfilled either synchronously or asynchronously. A resource method set contains resource-specific methods for manipulating a type of resource by a kernel-mode client, and is used in resource allocation by enumerated devices on a bus.

A public high speed network, operating at 100Mbps, capable of voice and data transmission over a distance of up to 50 miles.

microcomputer

Any computer based on a single-chip processor.

microkernel

An alternative kernel design developed by researchers at Carnegie-Mellon University and implemented in the Mac OS. It has been stripped down to the point where it is only concerned with loading, running, and scheduling tasks. All other OS functions(virtual memory management, disk I/O, etc.) are implemented and managed as tasks running on top of the microkernel.
Traditionally, the kernel has been a monolithic piece of the OS, resident in memory at all times, taking care of operations as varied as virtual memory management, file I/O and task scheduling.

micron

A unit of measurement. One millionth of a meter, corresponding to approxiamately 1/25,000 of an inch. The core diameter of fiber optic network cabling is often specified in terms of microns,62.5 being a common size.

microprocessor

Often called a processor, a CPU on one single chip. The first microprocessor was developed by Intel in 1969. The microprocessors most often used in PCs are the Motorola 680X0 series used in the Apple Macintosh computers, and the Intel 80x86 family used in IBM and IBM-compatibles.

Microsoft Diagnostics program that comes with Windows 3.1 and later versions of DOS. It can help you identify what's in a PC, as well as possible hardware problems. However, it does not correctly identify Pentium or 586 processors, so don't worry if if says you have a 486!

Microsoft DirectShow

Formerly ActiveMovie™. A cross-platform API for developers of multimedia applications that provides a user-mode connection and Stream architecture to support high-quality digital video, high-fidelity audio, and special effects.

Microsoft DirectX®

A low-level API that provides user-mode media interfaces for games and other high-performance multimedia applications. DirectX is a thin layer, providing direct access to hardware services, and takes advantage of available hardware accelerators and emulates accelerator services when accelerators are not present.

A port that allows the connection of a musical instrument digital interface(MIDI) device to a PC.
The three types of port described in the standard are MIDI In, MIDI Out, and MIDI Thru. A synthesizer receives MIDI messages via its MIDI In port, and forwards messages to other devices using the MIDI Thru port. It can send its own messages to the computer using the MIDI Out port.

Multipurpose Internet Mail Extensions. A set of extensions that allows the Internet e-mail users to add non-ASCII elements such as graphics, PostScript files, audio, or video to their e-mail. Most of the common e-mail client programs include MIME capabilities.

MMX is not an acronym for anything, although it has been thought that the name evolved from either 'Multimedia Extentions' or 'Matrix Math Extentions' during development. MMX does, however, stand for something important. When you see this designation, it means that the processor inside the computer has been equipped to handle multimedia tasks more efficiently. This will result in smoother and more realistic video and audio effects.
One important catch is that the software you are using must be specially programmed to take advantage of the MMX technology for you to see a significant performance boost.

minicomputer

A medium-sized computer system capable of managing over 100 users simultaneously, suitable for use in a small company or single corporate or government department.

minidriver

A hardware-specific DLL that uses a Microsoft-provided class driver to accomplish most actions through function calls and provides only device-specific controls. Under WDM, the minidriver uses the class driver's device object to make system calls.

miniport driver

A device-specific kernel-mode driver linked to a Windows NT, Windows 2000, or WDM port driver, usually implemented as a DLL that provides an interface between the port driver and the system.

Acronym for million of instructions per second. A measure of the processing speed of a computer's CPU.

MIPS R4000 and R4400

A family of 64-bit microprocessors from MIPS Computer Systems. The R4000 has a 1.3 million transistor design, with both an 8K data cache and an 8K instruction cache, as well as a floating point processor. Internally, the R4000 runs at 100 MHz, double its external 50-MHz clock output. The R4400, with 2.2million transistors, is based on the R4000, but has larger cache units (16K data cache and 16K instruction cache), and runs internally at 150 MHz, externally at 75 MHz. Silicon Graphics acquired MIPS in June of 1992.

mixer class

The class of filters that deal with manipulating controls such as volume, treble, and so on.

modem

Contraction of modulator/demodulator, a device that allows a computer to transmit information over a telephone line.
The modem translates betweent he digital signals that the computer uses, and analog signals suitable for transmission over telephone lines. When transmitting, the modem modulates the digital data onto a carrier signal on the telephone line. When receiving, the modem performs the reverse process, and demodulates the data from the carrier signal.

The most widely used method of storing data on a hard disk. Based on an earlier technique known as frequency modulation (FM) encoding, MFM achieves a two-fold increase in data storage density over standard FM recording, but it is not as efficient a space saver as run-length limited encoding.

modulation

In communications, the process used by a modem to add the digital signal onto the carrier signal, so that the signal can be transmitted over a telephone line.
The frequency, amplitude, or phase of a signal may be modulated to represent a digital or analog signal.

monitor

A video output device capable of displaying text and graphics, often in color.

monochrome monitor

A monitor that can display text and graphics in one color only(i.e.; white on black,etc.)

Mosaic

A graphical WWW browser.

motherboard

The main printed circuit board in a computer that contains the CPU, appropriate coprocessor and support chips, device controllers, memory, and also expansion slots to give access to the computer's internal bus.

mouse

A small input device with one or more buttons used as for pointing or drawing.

MS-DOS

Microsoft Disk Operating System. MS-DOS allocates system resources such as hard and floppy disks, the monitor and the printer to the applications programs that need them.
MS-DOS is a single-user, single-tasking operating system, with either a command-line interface, or a shell interface. Its is the most ubiquitous OS ever written, running over 20,000 different applications programs on an estimated 60 million computers.

MSDOS.SYS

A hidden system file that loads on boot and provides basic DOS functions to a PC.

multicast addresses

One of the addresses that IPv6 reserves for special purposes. Multicast addresses begin with FF**:-- while a unicast address identifies one NIC, a multicast address identifies a group of NICs for a group of computers. If a packet is sent to a multicast address, all the members in the group receive that packet.

multilayer

A printed circuit board that contains several different layers of circuitry. The layers are laminated together to make a single board, onto which the other discrete components are added.

multimedia

A computer technology that displays information using a combination of full-motion video, animation, sound, graphics and texts with a high degree of user interaction.

Abbreviated MPC. The Multimedia PC Marketing Council, consisting of several hardware and software vendors sets standards for multimedia PCs and the software that runs on them.

multiple DOS configurations

DOS6 includes features that allow you to define different system configurations and choose the one you want to use at startup time.
To do this you define a startup menu in your CONFIG.SYS file, and then create configuration blocks for each selection in the startup menu. When your system starts, the menu is presented on the screen, you choose the selection you want to use, and your system is configured accordingly.

multiplexing

In communications, a technique that transmits several signals over a single communications channel.

Frequency-division multiplexing separates the signals by modulating the data into different carrier frequencies.

Time-division multiplexing divides up the available time between the various signals.

mux. In communications, a device that merges several lower-speed transmission channels into one hgih-speed channel at one end of the link. Another multiplexor reverses this process at the other end of the link to reproduce the low-speed channels.

multiprocessing

The ability of an OS to use more than one CPU in a single computer.

Symmetrical multiprocessing refers to the OS's ability to assign tasks dynamically to the next available processor; this ensures that each processor is being used fully.

Asymmetrical multiprocessing requires that the original program designer choose the processor to use for a given task at the time of writing the program. This approach is relatively easy to implement, but can result in some processors being busier than others.

multisync monitor

A monitor designed to detect and adjust to a variety of different input signals. By contrast, a fixed-frequency monitor must receive a signal at one specific frequency.

multitasking

The simultaneous execution of two or more programs in one computer.

multiuser

Describes a computer system that supports more than one simultaneous user. Unix and its derivatives are all multiuser systems.

MX

A DNS record type used with Set Type= command. Anacronym for Mail eXchanger, it is a computer that receives a mail on behalf of a computer and/or forwards it further on.
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mixer class

The class of filters that deal with manipulating controls such as volume, treble, and so on.

monolithic driver

A driver that has many different classes of functionality contained in the same driver.

MPEG

Moving Pictures Experts Group. Used when referring to one of several standard video-compression schemes. A codec for squeezing full-screen, VHS-quality digital video into a small data stream so it can be played from a CD-ROM drive.

MSDN

Microsoft Developer Network

MTD

Memory technology driver. A protected-mode driver that works with Windows protected-mode PC Card software to enable form-factor cards, such as flash memory cards. Such memory cards and their related drivers do not provide full Plug and Play capabilities

multifunction device

A piece of hardware that supports multiple, discrete functions, such as audio, mixer, and music, on a single adapter.